As a gemstone, diamond is known for its rarity and beauty. As an industrial material, its superior hardness and wear resistance make diamond a preferred material in a variety of applications. For example, diamond is used extensively as an abrasive in polishing operations, and diamond-tipped drills and cutting tools are indispensable in shaping extremely hard materials such as sintered carbide and quartz. To help meet the industrial demand for diamond, a number of techniques have been developed by others for the production of synthetic diamond. While natural diamond is still used in many industrial applications, diamond synthesis is emerging as the solution to the problem of inadequate supply of this unique material.
Diamond has a cubic lattice, with each carbon atom being covalently bonded to four other carbons to form a tetrahedron. This structure is repeated throughout the crystal and it is believed that this network of carbon-carbon bonds produces the extreme hardness of diamond which is unequalled by other materials. It was found that at high temperatures and pressures, the conversion of carbon to diamond occurs at an appreciable rate. This phenomenon gave rise to the first synthetic high-pressure diamonds in the early 1950's.
With the use of massive high-pressure presses and through another high-pressure technique--shock wave diamond synthesis--many tons of diamond grit are synthesized annually throughout the world. High-pressure techniques have also recently been used to synthesize relatively large single crystal diamonds which are laser cut to form heat sinks for electronic devices. It will be appreciated that diamond is useful in this type of application due to its high thermal conductivity.
Due in part to the numerous limitations inherent in high-pressure diamond synthesis processes, much effort has been made to develop alternative techniques. As a result, methods have been developed by which diamond thin films can now be formed on selected substrates. Diamond thin films are of significant interest to the electronics industry and, as will be appreciated by those skilled in the art, diamond thin films may be doped to produce n-type and p-type diamond layers.
Previous deposition experiments have established some of the preliminary techniques currently used in diamond synthesis. However, much development is needed to fabricate reproducable films reliably. This document presents such a new approach to reliable nucleation and growth of diamond materials. In the past, diamond was only able to be grown on selected substrates by the thermal or plasma decomposition of a single carbon-containing gas or a single mix of carbon-containing gases. For example, Eversole, Angus and others simultaneously deposited diamond and graphite on diamond seed crystals and then removed the graphite by hydrogen etching. Later, Russian workers utilized a mixture of methane and hydrogen based on Angus's work to produce a diamond film on a diamond substrate in a process in which hydrogen inhibited graphite formation. The graphite which did form was removed with an atomic hydrogen etch. These efforts were refined somewhat and finally resulted in the growth of diamond on non-diamond substrates.
Chemical vapor deposition of diamond has been achieved through the use of heated-filaments, direct current plasmas, RF plasmas and microwave initiated gas plasmas in both high and low pressure environments. The feedstock gas is typically a mixture of hydrogen and methane. The hydrogen component dissociates to form atomic hydrogen. The methane component also dissociates, presumably forming CH.sub.3 radicals which are believed to be instrumental in promoting diamond growth. In U.S. Pat. No. 4,767,608 to Matsumoto, the formation of bulk-form diamond on a substrate by electric plasma discharge is disclosed. It is also known to etch away a substrate to produce bulk-form diamond.
In particular, microwave plasma deposition of diamond has received considerable attention as a viable commercial system for producing diamond thin films. Typically, a frequency of 2.45 GHz is utilized to dissociate a feedstock gas mixture of hydrogen and a carbon source such as methane or acetylene. As previously stated, the microwave radiation dissociates the feedstock gases to produce atomic hydrogen and active carbon species. Typically, the process is carried out at pressures between 10 to 100 torr. The substrate is positioned on a heated support to maintain the substrate at a temperature of between about 500.degree. C. and 1,100.degree. C. Polycrystalline diamond films with some non-diamond carbon content can be formed in this manner over a large substrate area. The crystallites formed are typically between 25 nanometers and 25 microns in size.
As stated, non-diamond substrates have also been used successfully for the production of synthetic diamond films. Such substrates include several metals, for example, nickel, copper and titanium, as well as ceramics, carbides, nitrides, sapphire, silicon and graphite. Other non-diamond substrates are also known. As will be appreciated by those skilled in the art, a suitable substrate must provide sufficient nucleation sites to support adequate diamond growth.
To Applicant's knowledge, he is the first to utilize a vapor deposition process of diamond on a releasable substrate to form shaped diamond articles and to do so in a two-step, nucleation/growth process utilizing two different gas mixtures. Therefore, it is an object of the present invention to provide methods by which shaped synthetic diamond articles can be formed on releasable molds. It is a further object of the present invention to provide near-net shape synthetic diamond articles formed by vapor deposition of diamond on releasable molds. It is still a further object of the present invention to provide a method by which shaped synthetic diamond articles can be formed on adherent, etch-resistant molds by vapor deposition.